1. Field of the Invention
The present invention relates to a fundus photography apparatus, particularly to an eye fundus photography apparatus equipped with means for photographing the anterior ocular segment of the eye and means for photographing the eye fundus illuminated with a beam of light.
2. Description of the Prior Art
In order for a fundus photography apparatus to obtain good-quality images of the eye fundus, the fundus has to be illuminated with light of optimal intensity during the photography. Doing this requires an automatic exposure mechanism to detect the intensity of light reflected from the fundus and set the exposure accordingly. However, such an automatic exposure mechanism is so complex that generally an optimum reference exposure is set based on the photography conditions, pupil diameter, or past experience of the examiner and he or she corrects the set exposure for eye fundus photography.
When, for example, photography is performed using a high-magnification setting, the reference exposure is greater than when a low-magnification setting is used, and when the fundus camera has a digital type CCD, the reference exposure is greater than when an analogue type device is used.
However, people's eyes are infinitely varied, and the above exposure setting may not provide the best results. One factor in this is that the coloring of the fundus varies from person to person, so the reflectivity also varies. In order to take this into account, the examiner has to check the pupil color of the eye concerned and correct the exposure value based on his or her judgment.
Conventionally, the color has been detected from the fundus image. For example, spectral distribution of a light beam from a specific part of the fundus image is measured and the result is used to calculate and display the color information, as described in Japanese laid open patent publication No. 109032/91. Disclosed in Japanese Patent No. 3363520 is also a method in which the color of the iris is detected and a filter having a prescribed transmission characteristic corresponding to the detected color is selected to emphasize a pattern projected onto the anterior ocular segment of the eye. Japanese laid open patent publication No. 2003-10128 also discloses an arrangement in which the intensity of the observation light source and the gain of means for photographing the observed image are set to desired ones during observation of the anterior ocular segment of the eye.
However, with the conventional fundus photography apparatus, the exposure has to be adjusted according to the color of the iris of the eye, so in order to obtain good-quality fundus images, the examiner has to confirm the color of the eye each time and use his or her judgment to correct the exposure.
The object of the present invention is to provide a fundus photography apparatus that, when photographing an eye fundus, can adjust the exposure to an optimal value depending on the color characteristics of the anterior ocular segment of the eye.